City-dwellers are constantly exposed to pollution, which can contribute to heart and respiratory problems. But commuters may be getting a particularly big dose on their way to and from work. Drivers are breathing more polluted air, especially when diesel vehicles such as trucks and school buses are nearby, researchers say.

The team studied pollution exposure for one week in Montreal, three weeks in Toronto, and four weeks in Vancouver. In each city, researchers drove three Chevrolet Grand Caravans on highways, downtown streets, and suburban roads during weekday rush hours. The vehicles were outfitted with instruments to monitor pollutant levels inside and on the roof of the car, and the drivers kept the windows closed and the fan speed on medium.

While driving, the team members noted traffic levels and the number of diesel vehicles nearby on a voice recording. Later, they compared the in-vehicle and rooftop pollutant levels to regional outdoor measurements taken during commute hours.

The levels of two pollutants — nitrogen dioxide and fine particulate matter — tended to be similar inside and on the rooftops of the cars, the authors found. The in-vehicle concentrations of those pollutants were also higher than the regional readings. The more diesel vehicles the drivers saw nearby, the higher the in-vehicle levels of fine particulate matter, ultrafine particles, and black carbon, and the higher the ratio of in-vehicle to rooftop pollutant levels.

Since the study authors used only one type of car, they can’t say whether their findings apply to all vehicles. Researchers will also need to find out how the ventilation settings, such as the fan speed, affect pollutant levels in the car. — Roberta Kwok | 18 December 2014